The polymers contemplated by this invention are disclosed in U.S. Pat. Nos. 4,320,224; 4,360,630; and 4,446,294, the entire disclosures of which are incorporated by reference. These crystalline, linear polymers contain in the polymer chain at least 50 percent of the following repeating unit (hereinafter referred to as "repeating unit I"): ##STR2## The polymers may be composed solely of repeating units I or may contain other repeating units as hereinafter defined and they have inherent viscosities IV (measured at 25.degree. C. in a solution of the polymer in concentrated sulphuric acid of density 1.84 g cm.sup.-3, said solution containing 0.1 g of polymer per 100 cm.sup.3 of solution) of at least 0.7. These polymers are exceptionally useful in that they possess excellent mechanical and electrical properties, coupled with outstanding thermal and combustion characteristics. They also show resistance to a very wide range of solvents and proprietary fluids. They are thus very suitable in applications where the service conditions are too demanding for the more established, high performance polymers and in particular where the polymers are liable to high service temperatures.
In view of the foregoing desirable properties of these particular aromatic polyetherketones, it would be advantageous if they could be easily formed into filaments and fibers since the latter products could then be made for example into knitted, woven and non-woven fabrics, fiberfill and insulation products suitable for applications utilizing their excellent physical and chemical properties. However, the same combination of properties which would make filaments and fibers made from these polymers very desirable in various applications, e.g. heat and solvent resistance, also cause them to be very difficult to spin into such filaments and fibers, particularly those of relatively low denier. Thus, if it is attempted to melt spin these polymers into filaments in a conventional manner, the use of a relatively low spinning temperature results in a high melt viscosity which significantly reduces spinning stability due to high spinning pressures, clogging of the spinneret holes, uneven polymer coagulation and frequent filament rupture. On the other hand, unduly high spinning temperatures result in polymer degradation and cross-linking which cause void, gel and speck formation in the filaments and render them unsuitable for most uses. In view of these factors, successful spinning into filaments of the polymers contemplated by this invention, particularly filaments of relatively low denier, is not easily accomplished. Although U.S. Pats. Nos. 4,320,224, and 4,446,294 disclose broadly that polymers containing a major proportion of repeating unit I may be fabricated into any desired shape including fibers, they do not have any specific teaching of how such fibers may in fact be formed.